All material creations take place from subtle to gross. The entire universe has developed in that manner. From the sky developed the touch sensation, which is a mixture of eternal time, the external energy and the glance of the Personality of Godhead. The touch sensation developed into the air in the sky. Similarly, all other gross matter also developed from subtle to gross: sound developed into sky, touch developed into air, form developed into fire, taste developed into water, and smell developed into earth.